Known thermoforming foamed sheets include a polystyrene resin foamed sheet containing a large quantity of an inorganic fine powder as disclosed in U.S. Pat. No. 4,426,065 and a polypropylene resin foamed sheet containing a large quantity of an inorganic fine powder as disclosed in JP-A-60-141728 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"). Since the polystyrene resin foamed sheet is poor in heat resistance and oil resistance, formed articles such as trays and containers obtained therefrom are incapable of use in a radar range, and the sheet is unsuitable for producing deep draws such as cups. Further, it is poor in impact resistance and tensile strength.
The above-stated polypropylene resin foamed sheet shows improved heat resistance permitting of use in a radar range and improved deep drawing properties as compared with the polystyrene resin foamed sheet. However, when the sheet having printed thereon a prescribed pattern is subjected to thermoforming, the pattern is liable to be shifted or deformed each time it is formed. Further, when the extruded sheet is taken off along a drum, it shows resistance against the cylindrical drum to slow down the take-off speed or cause tearing of the sheet.